Mobile chair base



FIG. 1 is a perspective view of a mobile chair base showing my newdesign;

FIG. 2 is a side elevational view;

FIG. 3 is an elevational view showing the side opposite that shown inFIG. 2;

FIG. 4 is a bottom plan view; and

FIG. 5 is a top plan view thereof.

The ornamental design for a mobile chair base, as shown and described.